boost.asio's socket's receive/send functions are bad?

Question

Data may be read from or written to a connected TCP socket using the receive(), async_receive(), send() or async_send() member functions. However, as these could result in short writes or reads, an application will typically use the following operations instead: read(), async_read(), write() and async_write().

I don't really understand that remark as read(), async_read(), write() and async_write() can also end up in short writes or reads, right?
Why are those functions not the same?
Should I use them at all?
Can someone clarify that remark for me?

Answer 1

The read, async_read, write, and async_write are composed functions that call the class functions multiple times until the requested number of bytes is transmitted. They are included by the library as a convenience. Otherwise, every developer would need to implement the same logic.

The class functions wrap the underlying OS functions directly, which basically state in the documentation: these functions may return before all of the bytes are transmitted.

In most cases, you should use the free (composed) functions to transmit data.